In a field of an optical disk drive, a DVD (Digital Versatile Disc) has been generally used as a recording medium, and now use of a BD (Blu-ray Disc) begins to spread. BD still further increases recording density and therefore increases recordable time in video recording or the like. On the other hand, stricter specifications are set forth for components including an optical pickup. For example, change in characteristics depending on temperature is strictly specified.
Therefore, a plastic lens is hardly used for an objective lens of an optical pickup for BD since it has significantly variable characteristics including spherical aberration, and a glass lens is used for the objective lens. BD is different in this point from DVD or CD, which has been a problem for achieving cost reduction. To correct a temperature characteristic of an objective lens, it is first necessary to accurately know temperature of the objective lens. Although a typical optical pickup has a temperature sensor, the sensor is not always provided in a position at which the sensor may accurately measure temperature of an objective lens.
On the other hand, patent document JP-A-2008-97775 discloses a method where an objective lens is attached to a lens holder via a fixing member having high heat conductivity, and a temperature sensor is provided on the fixing member to accurately determine the temperature of the objective lens.